Foreign materials may be generated due to several reasons in a manufacturing process of a transparent substrate having a thin thickness, a packaging process, a pattern forming process using the transparent substrate, and the like. In the case in which the foreign materials generated in these process environments are attached onto an upper surface of the substrate, they hinder fine patterns for pixels from being formed on the upper surface in the subsequent process to allow circuit patterns for forming the pixels not to be formed at corresponding positions, thereby causing defective pixels and decreasing a process yield. Therefore, a process of inspecting the foreign materials on the upper surface of the substrate should be performed during or after the manufacturing process.
A lower surface of the substrate contacts a transporting means in order to transport the substrate in a manufacturing process of a flat panel display (FPD) and a semiconductor. Therefore, much more foreign materials may be attached onto the lower surface of the substrate than onto the upper surface of the substrate. Since fine foreign materials having sizes smaller than those of pixels among the foreign materials on the lower surface of the substrate do not have an influence on characteristics of the pixels, the fine foreign materials on the lower surface of the substrate are permitted. Therefore, only the foreign materials on the upper surface of the substrate have been strictly inspected in the manufacturing process of the transparent substrate and the manufacturing process of the FPD and the semiconductor using the transparent substrate.
In the manufacturing process of the FPD and the semiconductor, in order to inspect the foreign materials, a vision inspection method using an image obtained by irradiating light and imaging reflected light by a camera among non-contact inspection methods that do not damage the surface of the substrate has been mainly used. In the case of using the transparent substrate, the light arrives at the lower surface of the transparent substrate, such that reflected light on the foreign materials on the lower surface is also transferred. Therefore, the foreign materials on the lower surface are imaged, thereby making it possible to make an excessive badness decision and have an influence on a manufacturing yield. Therefore, a method of inspecting only the foreign material on the upper surface without being affected by the foreign materials on the lower surface has been required.
In FIG. 1, a schematic view of a foreign material detecting device 10 of a transparent substrate having a thickness exceeding 0.3 T according to the related art is illustrated. Existing methods for detecting a foreign material on an upper surface UG of a transparent substrate G will be described with reference to FIG. 1. An upper surface foreign material and a lower surface foreign material of the transparent substrate G are distinguished from each other through an upper surface detecting part UD irradiating light L at an inclined angle θ so as to irradiate the light to both of the upper surface UG and a lower surface LG of the transparent substrate G, thereby inspecting scattered light of a first irradiation surface I1 irradiated to the upper surface UG of the transparent substrate G and a lower surface detecting part LD inspecting scattered light of a second irradiation surface I2 passing through the first irradiation surface I1 of the transparent substrate G, refracted, and then irradiated to the lower surface LG.
As illustrated in FIG. 1, in the case in which a thickness of the transparent substrate G exceeds 0.3 T, a section overlapped in a direction perpendicular to the transparent substrate G is not generated between the first irradiation surface I1 and the second irradiation surface I2, and is not also generated particularly between a third irradiation surface I3 on which light reflected on the lower surface LG is irradiated to the upper surface UG of the transparent substrate G and the second irradiation surface I2, such that the upper surface foreign material and the lower surface foreign material may be clearly distinguished from each other through the upper surface detecting part UD and the lower surface detecting part LD.
However, in the foreign material detecting device according to the related art as described above, in the case in which the transparent substrate is formed of an ultra-thin plate having a thickness of 0.3 T or less, the following problems occur.
In FIG. 2, a schematic view of a foreign material detecting device 20 of a transparent substrate having a thickness of 0.3 T or less according to the related art is illustrated.
As illustrated in FIG. 2, in the case in which the transparent substrate G is formed of an ultra-thin transparent plate, an overlapped portion OL is generated between the first irradiation surface I1 on which the light is irradiated to the upper surface UG of the transparent substrate G, the second irradiation surface I2 on which the light passing through the first irradiation surface I1 of the transparent substrate G and then refracted is irradiated to the lower surface LG, and between the second irradiation surface I1 and the third irradiation surface I3 on which the light reflected on the second irradiation surface I2 is irradiated to the upper surface UG. Particularly, since the overlapped portion OL covers the entire second irradiation surface I2, in the case of inspecting the second irradiation surface I2 by the lower surface detecting part LD, the second irradiation surface I2 is overlapped with the first and third irradiation surfaces I1 and I3, such that it is impossible to distinguish whether a foreign material is a foreign material present on the upper surface UG of the transparent substrate or a foreign material present on the lower surface LG of the transparent substrate.
Therefore, the development of a device for detecting only the foreign material on the upper surface of the transparent substrate having a thickness of 0.3 T or less has been demanded.